39-40 Buick voltage regulator identification

[buick looks fine for 39]

After a 10 year restoration a friend is going to start up his 39 Buick 40 series. My concern is he might have a 40 Buick voltage regulator rather than a 38-39. As I understand it the part number is 309 which does not coincide with any reference numbers I have.  How a person can identify  a 38-39 from a 40-47 Buick voltage regulator by looking at them ?  

 

Thanks

 Leif

[Bloo]

How many relays inside?

 

Regulator all series

1939:  5858

1940:  1118201

 

Generator 40 series

1939:  1101052

1940:  1102662 w/4.4 axle

1940:  1102663 w/3.9 axle

 

With pictures maybe I could guess. The trouble is, regulators of a given "type" look all the same no matter what they are for.

 

If I remember correctly, 1939 was still a 3rd brush split field generator with a 2-unit regulator, and 1940 was a 2 brush with a 3-unit regulator.

 

Some old pics of a 5858 (1939) from Ebay:

 

 

 

 

and 1118201 (1940):

 

 

 

 

Edited June 6, 2020 by Bloo (see edit history)

[buick looks fine for 39]

Thank you bloo, that was very helpful, now I know what I'm looking for.